BI111 Lecture Notes - Lecture 2: Base Pair, Silent Mutation, Allele

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11 Jan 2016
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Lecture 2 – Wednesday January 6, 2016
The Road To The Phenotype
Introns removed from Pre-mRNA before translation
Alternate mRNA transcripts created by selective
slicing/arrangement of exons
mRNA is the rst step in producing the phenotype
1. Transcription
2. RNA processing
3. Translation
oGenetic code is translated into amino acids
oThere are corresponding amino acids where translation
should start and stop
The genetic code has both specicity, and redundancy
oEvery word has an amino acid
oSeveral words mean the same thing
Genetic code was established very early in the evolution of life
and has remained unchanged
4 Classes of Mutations
oMissense mutation
Single base-pair has been mutated
Altered sense codon
Altered amino acid
Changes one of the letters in the word, so it is
referring to a di+erent amino acid
oNonsense mutation
Base-pair is mutated
Codon changed to stop translation
Premature termination of polypeptide
oSilent mutation
Base-pair changes, changes genotype but not
phenotype
Codon changed to another for same amino acid
No change in amino acid
oFrameshift mutation
Insertion of a base pair
Reading frame o+ by one from here on
Amino acids altered due to frameshift
Mutations Can A"ect Phenotype
Ex. Sickle-cell disease
oT is changed to U, and therefore the amino acid is changed
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